The present invention relates to a vessel for a high pressure discharge lamp and a method of manufacturing the same. The present invention also relates to a high pressure discharge lamp having such a vessel and a method of manufacturing the same.
Such a vessel is generally classified into two types. The vessel according to a first type is called as xe2x80x9cintegrated type vesselxe2x80x9d and has a main portion forming a discharge space and end portions integrated into the main portion. The vessel according to a second type is called as xe2x80x9cassembled type vesselxe2x80x9d and has a main portion and separate end portions which are inserted into the respective openings of the main portion and thereby assembled with the main portion. However, the assembled type vessel cannot be used for a low watt type of high pressure discharge lamp because of a low lamp efficiency due to the heat loss at junctions of the main portion and the respective end portions. The assembled type vessel cannot be used for a high pressure discharge lamp either, because lamp efficiency is an important factor even for a middle-high watt type of high pressure discharge lamp. Therefore, when such lamps are to be manufactured, it has been considered necessary to use the integrated type lamp which does not suffer from the above-mentioned disadvantage of the assembled type vessels.
It is desirable that the transmittance of the lamp is as high as possible, so that at least a central area of the main portion of the vessel should be as thin as possible. On the other hand, it is desirable that the mechanical strength of the end portions to be inserted by the respective electrode members is as high as possible, so that the thickness of the end portions should be as large as possible. Also, as a light-emitting material tends to be collected and the proceeding of corrosion is fast in the neighborhood of boundary areas between the respective end portions and the main portion, it is preferable that the thickness of the neighborhood is as large as possible to mitigate adverse influence of corrosion and achieve prolonged lifetime. Therefore, by using a vessel having an entirely uneven thickness wherein main portion has a thickness at the central area which is smaller than at the respective end portions and at the boundary areas between the respective end portions and the main portion, it is possible to manufacture the lamp having a prolonged lifetime as compared to the lamp with a vessel having an entirely uniform thickness.
Conventionally, when the integrated type vessel is formed with a blow molding of the vessel as disclosed in JP-A-10-81183, for example, as shown in FIGS. 1A and 1B, a tubular shaped body 1 (FIG. 1A) made of a transparent or translucent ceramic material such as alumina is arranged between an upper half 2 and a lower half 3 of the mold, these mold halves 2, 3 are moved toward each other as shown by arrows a and b, respectively, to set the shaped body 1, and a pressure atmosphere such as air is introduced into an opening 4 of the shaped body 1 so as to obtain a blow-molded body 5 (FIG. 1B) of the vessel.
In the case of the blow molding process, it is possible to manufacture a vessel in which at least the central area of the main portion has a thickness smaller than at the respective end portions and at the boundary areas between the respective end portions and the main portion. However, it is necessary for the opening 4 to have a diameter enough to admit air into the opening 4. As a result, it is difficult for the inner diameter of the respective end portions to have a diameter smaller not more than a designated value of 2 mm, for example. Even if it is possible, it is still difficult for the main body of the vessel to keep a necessary inner diameter of 1-15 mm, for example.
In the case of the casting process disclosed in JP-A-7-107333, for example, as shown in FIGS. 2A to 2C, after a slurry 9 has been introduced into the mold 6 (FIG. 2A) from an opening 7 and coated over the inner surface 8 of the mold 6 (FIG. 2B), the excess slurry 9 is removed so as to obtain a molded body 10 (FIG. 2C).
In this case, it is possible to preserve the opening 7 with a diameter not more than 2 mm (but not less than 0.8 mm), since it is only necessary for the opening 7 to secure a diameter enough to remove the excessive the slurry 9. However, because of the nature of the casting process, it is impossible to form a vessel in which at least the central area of the main portion has a thickness smaller than at the respective end portions and at the boundary areas between the respective end portions and the main portion.
It is an object of the present invention to provide an improved vessel which mitigates the above-mentioned limitations of the prior art and has an uneven thickness as a whole so that at least the central area of the main portion has a thickness smaller than at the respective end portions and at the boundary areas between the respective end portions and the main portion.
It is another object of the present invention to provide a high pressure discharge lamp which has such an improved vessel.
It is still another object of the present invention to provide a method of manufacturing such an improved vessel and a method of manufacturing such a high pressure discharge lamp.
The vessel according to the present invention comprises a main portion forming a discharge space, and end portions to be inserted into respective electrode members, the main portion and the end portions being integrally made of a transparent or translucent material, at least a central area of the main portion having a thickness smaller than at the respective end portions and at boundary areas between the respective end portions and the main portion, and an inner diameter of respective end portions is not more than about 2 mm.
According to the present invention, at least a central area of the main portion has a thickness smaller than at the respective end portions, so that the central area has a relatively high transmittance and the mechanical strength is relatively high when gaps between the respective end portions and the respective electrode members are sealed with glass. As already described, the light-emitting material tends to be collected and the proceeding of corrosion is fast in a neighborhood of boundary areas between the respective end portions and the main portion, however, because the central areas of the main portion have a thickness smaller than at the boundary areas between the respective end portions and the main portion, the adverse influence of the corrosion is smaller than the case where it has a substantially uniform thickness as a whole. As a result, the life time of the vessel according to the present invention is prolonged as compared to that of a vessel which has a substantially uniform thickness as a whole and is manufactured by the casting process. Therefore, a lamp having the vessel according to the present invention has a prolonged lifetime.
In manufacturing a lamp having the vessel, as the diameter of the respective electrode members to be inserted into the respective end portions get larger, the heat loss becomes higher when the lamp is operated, and thus the lamp efficiency is aggravated. Such an adverse influence is remarkable especially when the integrated type vessel for low watt is used, and it is desirable to keep the diameter of the respective electrode members at a necessary minimum length. However, if the inner diameter of the respective end portions is much larger than the diameter of the respective electrode members, the light-emitting material can easily penetrate into the gaps between the respective end portions and the respective electrode members after manufacturing the lamp, and the color of the light emitted from the lamp may change, for example. Therefore, the gaps should be as small as possible, that is, if the inner diameter of the respective end portions is not much larger than the diameter of the respective electrode members in view of the characteristics (color, efficiency) of the lamp. As a result, the inner diameter of the respective end portions should be not more than about 2 mm.
The vessel according to the present invention is suitable for the low watt (e.g. 10 W, 20 W, 50 W) type of the lamp. It is also suitable for the middle watt (e.g. 70 W, 100 W, 150 W) type of the lamp and the high watt (e.g. 250 W, 400 W) type of the lamp in which the lamp efficiency is an important factor. However, if the middle or high watt type of the lamp is used for another type of the lamp in which color rendering is an important factor, for example, it is possible to improve the lamp efficiency and the lifetime as compared to the lamp having the vessel whose thickness is substantially uniform as a whole.
Preferably, the ratio of an axial length of the respective end portions to the inner diameter of the respective end portions is not less than 4. Thereby, it is possible to mitigate the thermal stress resulting from the difference between the thermal expansion of respective end portions and that of respective electrode members, and thus improve the reliability at sealing portions of the respective end portions.
As already described, in manufacturing the lamp having the vessel, as the diameter of the respective electrode members to be inserted into the respective end portions get larger, the heat loss becomes higher when the lamp is operated, therefore the lamp efficiency is aggravated. To prevent such an aggravation, the outer diameter of the area of the respective end portions neighboring the main portion should be not more than about 4 mm.
The lamp according to the present invention comprises a vessel, which itself comprises a main portion forming a discharge space, and end portions to be inserted respective electrode members. The main portions and the end portions are integrally made of a transparent or translucent material, at least a central area of the main portion has a thickness smaller than at the respective end portions and at boundary areas between the respective end portions and the main portions, and an inner diameter of respective end portions is not more than about 2 mm.
As the lamp according to the present invention has such a vessel, the limitation of the inner diameter of the respective end portions is smaller than that of the conventional vessel, the transmittance of at least the central area of the main portion becomes high, the lifetime of the lamp is prolonged, and good characteristics (color, efficiency) are obtained.
Furthermore, in order to mitigate the thermal stress resulting from the difference between the thermal expansion of respective end portions and that of respective electrode members, and improve the reliability at the sealing portions of the respective end portions, the ratio of an axial length of the respective end portions to the inner diameter of the respective end portions may be not less than 4. Also, in order to prevent the aggravation of the lamp effect, the outer diameter of areas of the respective end portions adjacent to the main portion may be not more than about 4 mm.
There is also a method of manufacturing a vessel for a high discharge lamp, the vessel comprising a main portion forming a discharge space, and end portions to be inserted respective electrode members, the main portion and the end portions being made of a transparent or translucent material. The method comprises the steps of setting a tubular member made of a transparent or translucent material into a mold, the mold being air permeable at least locally, and decompressing a space between an outer face of the tubular member and an inner face of the mold with at least one portion of the mold being heated or cooled, to thereby bring the tubular member into contact with the mold so that the member has an outer shape which coincides with the inner face of the mold.
According to the present invention, the tubular member made of a transparent or translucent material is set into the mold which is air permeable at least locally, the space between the outer face of the tubular member and the inner face of the mold is compressed with at least one portion of the mold being heated or cooled, to thereby bring the tubular member into contact with the mold so that the member has an outer shape which coincides with the inner face of the mold. As the vessel has such a shape, the limitation of the inner diameter of the respective end portions is smaller than that of the conventional vessel, and it is possible to keep the inner diameter of the main portion at not more than 2 mm which cannot be realized in conventional manner.
The vessel manufactured by the method of the present invention is suitable for the low watt type of the lamp. It is also suitable for the middle watt type of the lamp and the high watt type of the lamp in which the efficiency is an important factor. However, if the middle or high watt type of the lamp is used for another type of the lamp in which the color rendering is an important factor, for example, it is possible to improve the lamp efficiency and the lifetime compared with the lamp having the vessel whose thickness is substantially uniform as a whole.
Preferably, the member, which has been brought into contact with the mold, is subjected to stretching so that at least a central area of the main portion has a thickness smaller than at the respective end portions and at boundary areas of the respective end portions and the main portion. Thereby, the central area has a high transmittance and a prolonged lifetime.
Preferably, in the setting step, the inner diameter of a portion of the member corresponding to the respective end portions is not more than about 2 mm. Thereby, the characteristics of the lamp is improved.
Preferably, the member, which has been brought into contact with the mold, is subjected to stretching so that a ratio of an axial length of the respective end portions to the inner diameter of the respective end portions is larger than 4. Thereby, it is possible to mitigate the thermal stress resulting from the difference between the thermal expansion of the respective end portions and that of the respective electrode members, and thus improve the reliability at the sealing portions of the respective end portions.
Preferably, the outer diameter of the respective end portions adjacent to the main portions is reduced furthermore after the member is molded into a certain shape. More preferably, the outer diameter is not more than about 4 mm. The aggravation of the lamp efficient is prevented in such a way.
Moreover, the lamp can be manufactured by inserting the respective electrode members into the respective end portions of the vessel manufactured by the above-mentioned method.